Double locking combination locks have been proposed in which a combination padlock is also capable of being opened by key. The use of steel balls to engage and lock shackles of combination locks has been proposed in prior patents (see U.S. Pat. Nos. 2,931,204 and 3,855,824). Arrangements for upsetting a permutation wheel during closing and locking a padlock has been proposed.
None of the prior proposals or uses has provided a satisfactory lock with the strength, security and reliability of the present invention.